Get to the route of why the turbo has failed/failing.It is very rare they will fail through wear and tear. Usually the fault lies with a blocked oil feeder pipe or issues around the oil pump not feeding the oil through. The turbo then is starved of oil, so that is why it goes in most cases. You don't want to be in the same situation in three to six months time.

I have also another car (honda) and the turbo made the same noise.It failed recently and unfortunately the AA warranty(not worth the paper written on) wouldn't cover it, claiming wear tear, so you've done we'll with BMW